It will be appreciated that during the operation of an internal combustion engine having pistons reciprocating in cylinders, that uncombusted gases will pass through the gap between the outer diameter of the piston and the wall of the cylinder. This gap between the piston and cylinder at the head or top land ring area of the piston is generally called crevice volume. It is an accepted fact that a portion of the unburned gases that are allowed to pass into the crevice volume are exhausted from the engine as unburned or partially burned gases, creating undesirable emissions, considered pollutants to the environment. This gap exists partly to accommodate the thermal expansion of the head of the piston (1) in the hottest possible case and (2) the most distorted or unround cylinder of a multi-cylinder engine. This required clearance at the outer diameter of the piston is accentuated by the machining tolerance capability of the piston manufacturer such that the largest potential machined size is normally less than the size required to eliminate touching or seizing in the cylinder in any of the cylinders of a multi-cylinder engine during the hottest operation as predicted in any projected engine operation in any typical climate. This clearance also results in undesirable piston motion occurring during the operation of the engine due to manufacturing tolerances of the piston skirt and the cylinder size allowing the piston to move laterally and rock or tilt in the cylinder, increasing crevice volume.
The only attempts of which I have knowledge to solve the above problem have been to develop techniques for more accurately machining the pistons and cylinders to tighter specific dimensions. However, machining tools wear while machining the pistons, which results in the same tool eventually machining pistons of different diameters. For example, a typical piston with a nominal diameter of 80 mm will be supplied in three "grade" sizes, equating to three diameter ranges. For example:
______________________________________ Grade Size Range ______________________________________ A 79.976-79.992 mm B 79.992-80.007 mm C 80.006-80.016 mm ______________________________________
This variation in piston sizes leads to a wide variation in piston to bore clearance. To my knowledge there has been no success in solving the above problem.